We’re planning on powering the pi directly to the 5V 2A slot on the VRM but we just wanted to make sure this was enough current because some documentation we’ve seen says 5V 3.1A. Also, we were thinking of using the 2 and 6 pin, as per this diagram (https://www.raspberrypi-spy.co.uk/2012/06/simple-guide-to-the-rpi-gpio-header-and-pins/), to power it with, so would these pins work if plugged into the VRM? Thanks so much!
If the documentation says that the pi needs 3.1 Amps, you shouldn’t plug it into the 5V/2A VRM port.
In any case, I always recommend that teams leave the VRM only for powering the radio and power any peripheral electronics from a separate voltage converter/regulator. The VRM is protected by a 20A fuse in the PDP; a short or over-current could blow that fuse and your robot will be a very expensive paperweight for the rest of the match. You can get voltage converters for pretty cheap from Amazon (like this), especially when you compare it to the price of losing a match.
alternatively, battery packs are legal which our team is trying to use to power our pi. We do not have the specific pack that we are using but I suggest that you would look in the manual and find what specs are legal and what is not.
If you are using a Pi4 (which we are), this is a nice alternative:
3 amps, USB-C connector, already potted in a case, small form factor, tabs for mounting with #10 screws, and all they want from you is $10.
There isn’t a whole lot not to like here…
– Chris Herzog - Joliet Cyborgs #4241
We were actually looking at the same one after a bit of searching! Did you find good results with it?
One way of doing it (it’s overkill if all you need is a power supply, but it’s got lots of other cool features you might find valuable) is a VMX-pi, which plugs directly into the robot battery, and has an onboard navX-sensor and CAN bus interface - and even has analog and digital I/O. On the software side, it’s got support for the WPI library as well (for off-season robot development).
So far so good - seems very solid and no undervoltage reports with hours of vision processing running (we’re running Chameleon Vision @ 640x480 at 30FPS with 3D solving enabled).
Yowza, that’s a sledgehammer full of functionality right there.
Where do you plug this in?
I have one PDP slot set aside for “custom” circuits so this is one of several on that chain. It has to be downstream of the PDP but you can essentially have as many “custom” circuits off of that one PDP connection up to the limit if that PDP slot.
We just got the power converter in the mail and really look forward to using it! Did you plug it into the PDP or the VRM while in use? I just wanted to make sure since both give off 12V and if I can save a spot on the PDP I’d like that
we power ours using a buck converter, there like 5 bucks off amazon.
I only run the radio off of the VRM - as it’s up to 3A, you don’t want it off of a VRM.
You can add another VRM but you’ll need to use a PDP slot. For general purpose use, the VRM just isn’t that useful so we use one PDP slot to power all our “custom” circuits; pi, vision lighting, some Canifiers, etc.
Don’t hang more off of the VRM you’re already using for the radio as it will not be able to supply enough current.
Even adding another VRM off of a PDP slot isn’t worth it, use that slot to power all your other custom stuff.
We then bought a USB C cable, which we soldered onto the output end of the converter. The converter shares a PDP slot with our LED controller.
Here’s our team’s experience with all the good ideas presented above.
The inexpensive buck voltage regulators didn’t work well for us as we were too often near brownout with heavy motor usage and the RPi voltage dropped too much below 5 v.
The CTRE VRM works great. The RPi doesn’t draw anywhere near 3.1 amps if above 5 volts with 2 HD-3000 cameras.
We also used last year with planned severe voltage drops with Mecanum drive the largest FRC legal Mophie Powerstation. It’s a great battery pack with well regulated voltage above 5 v. We tried some other battery packs but they all sagged below or never got to 5 volts. The RPi only likes the Morphie.
The RPi 3 normal power connector has a significant power drop from its fuse so we took our chances and used the GPIO pins (without any problems).
The RPi 4 normal power connector seems to be the same as using the GPIO pins.
We have had to power cycle the RPi a lot so make it easy to do that. We first soldered the power to the GPIO and that was a hassle - need a switch of some sort.